Bring Guinness to a boil in a small saucepan then simmer until it reduces to ½ cup; set aside to cool. In a double boiler, combine whole milk, sugar, and egg yolks and whisk together. Scrape seeds from vanilla bean halves and add both the seeds and the empty beans to the pan along with the molasses if using. Stir constantly until mixture thickens, then strain to remove any solids. Add cream and reduced Guinness to the mixture and refrigerate until chilled.
Process in an ice cream machine according to manufacturer's directions, then transfer to a covered container and freeze solid.
Recipe by Cooking With MicheleĀ® at https://cookingwithmichele.com/2010/07/guinness-ice-cream-yum/